NEW YORK — Despite all the worries about online bullying, more than two-thirds of teenagers on social-networking sites say their peers are mostly kind, a new study from the Pew Internet and American Life Project finds.

Still, 15 percent say they have been the target of mean or cruel behavior, and 88 percent say they have witnessed such behavior directed at others.

One-fifth of teens who use social-networking sites say they have personally joined in such bullying, and four-fifths say they defended someone who was a victim of meanness or cruelty. In all, 12 percent of all teens say they experienced bullying in the past 12 months, either in person, online or by text message or phone call.

The study, released Wednesday, also found that about 40 percent of parents of teens have friended their children on a social-networking site. But that tends to lead to more conflicts between parent and child over experiences on such sites.

The study’s co-author, Mary Madden, notes that children can present a limited profile to their parents and use private messaging channels to engage with friends.

Most teens say they employ privacy controls on social networks. Only 17 percent say that the profile they use the most is completely public.

The findings are based on a telephone survey of 799 teens and parents from April 19 to July 14. The margin of sampling error was plus or minus 5 percentage points. The portion covering 623 teens who use social-networking sites had a margin of error of 6 percentage points.

Printed on Thursday, November 10, 2011 as: Internet study reveals most teens consider peers on social-networking websites kind